chapter 7

• the periodic table is arranged by:

  -atomic number

  -groups and periods

  groups show the number of electrons in the outer shell

  periods show the highest energy electron shell
• periodicity is the repeating trend in properties of the elements
• the first ionisation energy is the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
• factors that affect ionisation energy:

  -atomic radius

  -nuclear charge

  -electron shielding
• the second ionisation energy is the energy required to remove one electron from each ion in one mole of 1+ gaseous ions to form one mole of 2+ gaseous ions
• the second ionisation energy is usually higher than the first, because when an electron is lost, nuclear attraction of the electrons to the nuclei increases, so atomic radius decreases as the electrons are pulled closer, so more energy will be required to remove the next electron,
• trend in ionisation energy down a group:

  -atomic radius increases and shielding increases, so

  -nuclear attraction on outer electrons decreases

  -so first ionisation energy decreases
• trend in first ionisation energy across a period:

  -nuclear charge increases, so nuclear attraction increases causing atomic radius to decrease

  -first ionisation energy increases
• however, the increase in ionisation energy across a period has two anomalies. there is a decrease from the filling of the s sub shell to the start of the filling of the p sub shell ( beryllium to boron). The other anomaly is where there is finally two electrons in one p orbital ( nitrogen to oxygen)
• ionisation energy decreases from beryllium to boron because the 2p sub shell has a higher energy level than the 2s sub shell, so the electron in the 2p shell is easier to remove
• ionisation energy decreases from nitrogen to oxygen because in oxugen there is one pair of electrons in a p orbital. this pair repel each other , making it easier to remove.
• metallic bonding is a special type of bonding for metals. each atom donates its outer shell electrons, leaving cations and delocalised electrons. Metallic bonding is the strong electrostatic force of attraction between cations and delocalised electrons.
• in a giant metallic structure, cations are fixed whereas delocalised electrons are mobile and are able to move throughout the structure.
• metals have high electrical conductivity in all states, as the delocalised electrons can carry charge throughout the structure.
• most metals have high mp and bp because high temperatures are necessary to provide the large amount of energy needed to overcome the strong electrostatic attraction between the cations and delocalised electrons
• metals do not dissolve
• non metals, boron carbon and silicon have different lattice structures. Billions of atoms are held together by a network of strong covalent bonds to form a giant covalent lattice.
• a giant covalent lattice has high mp and bp, due to strong covalent bonds that require a lot of energy to overcome
• a giant covalent lattice is insoluble in almost all solvents as the bonds are too strong to be broken by interactions with solvents
• giant covalent lattices are non conductors of electricity as there are no electrons left over for conducting charge. However graphene and graphite are exceptions as they can conduct electricity.